Method for determining chrysotile (asbestos) in the talc

ABSTRACT

A method is provided for determining the chrysotile content of talc comprising measuring the preferential adsorption of a sulfonphthalein dye, such as bromcresol purple (5,5&#39;&#39;-dibromo-ocresolsulfonphthalein) by chrysotile but not by talc. The final measurement is a spectophotometric determination of the dye remaining in solution after the adsorption step.

United States Patent [191 [111 3,881,822 Rose May 6, 1975 METHOD FORDETERMINING CHRYSOTILE (ASBESTOS) IN THE TALC Primary ExaminerRonald L.Wibert Assistant Examiner-Matthew W. Koren [75] Inventor. Harry A. Rose,Indianapolis, Ind. Attorney Agent or Firm Ralph w. Emsberger; [73]Assignee: Eli Lilly and Company, Indianapolis, Everet F. Smith Ind.

[22] Filed: Dec. 26, 1973 [57] ABSTRACT [21] Appl' 427778 A method isprovided for determining the chrysotile content of talc comprisingmeasuring the preferential [52] US. Cl 356/36; 356/201 adsorption of asulfonphthalein dye, such as bromcre- [51] Int. Cl. GOln 21/22 so]purple (5,5 -dibrom0-o-cresolsulf0nphthalein) by Field Search 201chrysotile but not by tale. The final measurement is a spectophotometricdetermination of the dye remaining References Cited in solution afterthe adsorption step.

UNITED STATES PATENTS 3,563,653 2/1971 Chen 356/36 12 Clams 1 DrawF'gure [BASE LINE m II U z x m a: o (I) ll- 2 .200

2 1 a, 1 '2 a a e I MG. CHRYSOTILE IN SAMPLE ADDED TO SAMPLE PATENTEDHAYsms w zkom mIo 92 COM I-IONVSHOSSV METHOD FOR DETERMINING CHRYSOTILE(ASBESTOS) IN THE TALC BACKGROUND OF THE INVENTION 1. Field of theInvention This invention relates to an analytical chemistry methodinvolving spectophotometry. More particularly, this invention relates toa method for determining the chrysotile content of talc bypreferentially adsorbing a sulfonphthalein dye on the chrysotile anddetermining the uptake of such dye by spectophotometric measurements.

2. Description of the Prior Art Talc is widely used in cosmetics andpharmaceuticals. When utilized as a diluent in pharmaceutical capsulesand tablets the talc is ingested by those taking the medicine.

Talc is a hydrated magnesium silicate which may be ideally representedas Mg (Ol-I) Si O It is often contaminated with other minerals such asquartz, dolomite, chlorite, and the various forms of asbestos. Asbestosin talc has been implicated recently by at least one investi gator as acause of stomach cancer in Japan. [Merliss, R. R., Science, 173, 1141-1142, (1971 Of the ashestos minerals, chrysotile is currently of mostphysiological concern.

Chrysotile is also a hydrated magnesium silicate which may be ideallyrepresented as Mg (OH) Si O The two minerals differ in their physicalstructure; talc being made up of more or less flat sheets of oxygen andhydroxyl moieties interspersed with magnesium and silicon atoms. Eachcomposite sheet is said to be electrically neutral. On the other hand,chrysotile has a ser pentine structure with an infinite number ofcrosslinked (Si O moieties and comprises a macroanion.

Several procedures have been proposed for determining the chrysotilecontent of talc. Mainly, these have been directed to such methods asX-ray diffraction and microscopic examination. X-ray diffraction becomesvery uncertain at low percentages of chrysotile in the talc. And opticalmicroscopic examination suffers because the particles approach the limitof resolution of the instrument.

Accordingly, it is an object of this invention to provide a simpleaccurate spectophotometric method for the determination of theconcentration of chrysotile in talc.

Still another object of this invention is to provide a spectophotometricmethod for the determination of the chrysotile content of talc which isreproducible through the use of an internal standard method obviatingthe need for a standard calibration chart.

SUMMARY It has now been discovered that chrysotile will quantitativelyadsorb such sulfonphthalein dyes as bromphenol blue, bromothymol blue,bromcresol green, bromcresol purple, cresol red, and thymol blue in thepresence of talc with no adsorption of such dyes by the talc. Theanalytical method based on this fact involves preparing a workingsolution of one of such dyes and spectrophotometrically measuring theadsorbance of such dye from the solution. Three samples of the talc tobe analyzed for the chrysotile content are accurately weighed and to twoof these samples are added accurately weighed differing quantities ofchrysotile and homogenous blends of such admixtures prepared. The threesamples are each contacted by the dye solution and thoroughly mixed. Analiquot of the supernatant from each sample is subjected. to aspectrophotometric absorbance measurement and such absorbances areplotted against the quantity of chrysotile added. By extrapolation to abaseline, the level of which is indicated by a blank, the chrysotilecontent of the talc is determined.

BRIEF DESCRIPTION OF THE DRAWING The accompanying drawing is a graphdepicting an illustrative curve obtained by plotting the residualabsorbance of a working solution of a sulfonphthalein dye after contactwith a sample of chrysotile containing talc against the quantity ofchrysotile added to such sample and extrapolating such curve to thebaseline absorbance of such working solution.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The novel method of thisinvention comprises selectively adsorbing a sulfonphthalein dye selectedfrom the class consisting of bromphenol blue, bromthymol blue,bromcresol green, bromcresol purple, cresol red, and thymol bluequantitatively on chrysotile in the presence of talc by contacting suchchrysotile containing talc with a solution of such dye andspectrophotometrically measuring the absorbance of such solutionfollowing such contact and graphically relating such absorbance with theabsorbance of such solution before such contact. Such dyes are notadsorbed by tale.

The sulfonphthalein dyes enumerated above by their common names arechemically described as follows:

Common Name Chemical Name Bromphenol blue 3,3 ,5 ,5'-tetrabromophenolsulfonphthalein Bromthymol blue3,3'--dibromo-thymolsulfonphthalein Bromcresol green3,3',5,5-tetrabromo-msulfonphthalein Bromcresol purple5,5'-dibromo-o-cresolsulfon phthalein Cresol red ocresolsulfonphthaleinThymol blue thymolsulfonphthalein The useful method of the instantinvention follows the steps of:

a. dissolving a sulfonphthalein dye selected from the class consistingof bromphenol blue, bromthymol blue, bromcresol green, bromcresolpurple, cresol red, and thymol blue in an appropriate water misciblesolvent and diluting such solution with an equal volume of water;

b. diluting the solution from a) with an acidic buffer to aconcentration that will yield after further dilution in the testprocedure an absorbance of from about 0.15 to about 0.75 at a wavelengthconsistent with the dye being utilized;

c. weighing accurately three samples of the talc to be analyzed tosimilar weights to the nearest 0.0010 g;

d. adding to one of the three samples from (c) an accurately weighedquantity of chrysotile equal to from about 0.5 to about 2.5 percent byweight of such sam- P e. adding to a second of the three samples from(c) an accurately weighed quantity of chrysotile equal to about twicethe concentration by weight added to the sample in (d);

f. adding to the third of the three samples from (c) and to the sampleprepared in (d) and (e) a volume of a 1:1 solution of ethanol-waterequal to at least twice the quantity of such sample;

g. providing a blank comprised of a volume of a 1:1 solution ofethanol-water equal to the volume of such solution added to each of thethree samples in (f);

h. subjecting the samples from (f) and the blank from (g) to anultrasonic treatment for about two minutes;

i. cooling the ultrasonically treated samples and blank from (h) to roomtemperature;

j. adding a portion of the dye solution from (b) to each of theultrasonic treated samples and blank from (i) in a volume equal to thevolume of the 1:1 ethanolwater solution added to such samples and usedas the blank;

k. mixing such dye solution thoroughly with such samples and blank andallowing the dispersions produced thusly to stand for about 30 minutes;

1. separating the liquid from the dispersions of (k) by firstcentrifuging and then filtering to remove all suspended solids leaving aclear filtrate;

m. removing an aliquot from the filtrate of (l) and diluting suchaliquot with about 1.5 volumes of an acidic buffer;

n. measuring the optical absorbance of the diluted filtrate of (m) at awavelength appropriate to the dye utilized in a suitablespectrophotometer;

o. plotting the absorbance against the amount of chrysotile added;

p. extrapolating a best fitting straight negative regression line to abaseline established as the absorbance of the blank of (g); and

q. determining the chrysotile concentration by reading the indicatedchrysotile content at the point where the negative regression lineintersects the baseline.

The useful sulfonphthalein dye selected from the class definedhereinbefore can be dissolved in such water miscible solvents asmethanol, ethanol, isopropanol, acetone, and the like, preferablyethanol. Generally from about 0.05 g to about 0.5 g of such dye isdissolved in about 150 ml to about 400 ml of the chosen solvent making asolution of from about 0.0125 to about 0.33 percent sulfonphthalein dye.After such dye is in solution an addition of water is made to provide astock dye solution of from about 0.01 to about 0.1 percent, preferablyabout 0.03 percent.

The stock solution is further diluted for use by taking an aliquot andadding additional water miscible solvent, water and an acidic buffer toprovide a concentration of dye that will yield, after further dilutionin the test procedure an absorbance of from about 0.15 to about 0.75 ata wavelength appropriate for the dye being used. Typically about ml ofthe stock solution is diluted with about 40 ml of the chosen watermiscible solvent and sufficient pI-I 4.2 acetate buffer to a totalvolume of about 250 ml. In the case of bromcresol purple such a solutionwill have an absorbance of 0.325 at 422p at a final concentration w/v ofabout 0.0012 percent.

Other useful sulfonphthalein dyes yielded the following absorbances whenprepared in solutions as described above.

Absorbance/ Wavelength m 11- Percent Concentration Dye Weight/VolumeBromphenol blue Not cletermi.. Not determined It is preferred to workwith relatively small samples of talc. Amounts of from about 0.1 g toabout 0.5 g generally providing sufficient material for reliableanalysis. Typically 0.2 g of talc is a convenient quantity. Largesamples can also be employed but usually offer little advantage. Theweighing of the samples should be done on a good analytical balance withan accuracy and precision of no less than 0.0010 g.

In the useful process of this invention a minimum of three samples oftalc are required. More can be utilized, but little if any benefitaccrues from increasing the number of samples beyond three. It is adecided benefit, however, to weigh each of the three samples to similarquantities, plus or minus 0.001 g. While such similarity of weightsmakes it simple to utilize this process, it is not imperative to havesuch precision as corrections can be made mathematically before plottingthe absorbances on the graph. A highly useful sample weight is 0.2000 i0.0010 g.

One of the three samples discussed immediately above is utilized withoutthe addition of pure chrysotile and to the other two samples are addedsufficient pure chrysotile to cause a significant variation in theabsorbance of the dye from the solution with which the sample iscontacted. A typical addition of chrysotile requires that each samplereceive a different quantity and it is a desirable situation to add onequantity which is twice the other. That makes the arithmetic plottingsimple and straightforward. Other ratios can be used and the eventualresults will be of similar reliability, but to do so only complicatesthe process. In practice it is desirable to add chrysotile in quantitieswhich will adsorb sufficient dye to reduce the absorbance by from about10 to about 50 percent. It was foundthat by adding 3 mg and 6 mgrespectively of chrysotile to 0.2000 g samples of talc containing about0.5 percent chrysotile reliable and reproducible determinations wereobtained when such samples were contacted with the working solution ofbromcresol purple as described hereinbefore. Other concentrations can beemployed with equal reliability, for example, an amount of chrysotileequal to from about 0.5 to about 5.0 percent of the tale in the samplecan be added to the latter and accurate absorbances measured from suchadditive samples. In any event, in plotting the absorbances it isadvantageous to make the plot absorbance v quantity to obtain aninterpolation of the quantity of chrysotile in the unspiked sample,which of course can then be converted to a percentage figure in theusual way.

After the accurately weighed chrysotile has been added to each of thetwo samples to be spiked, those two samples and the third unspikedsample are all treated with a volume of a 1:1 solution of the watermiscible solvent employed in dissolving the dye and water equal to from10 to fold the weight of the sample. In addition a volume of suchsolution equal to that added to the three samples is provided as ablank. Then all (four) of the thus provided samples are given anultrasonic treatment for two minutes. When samples of 0.2000 g of talcwere employed, ml ofa 1:1 solution of 95 percent ethanol and water wereadded to each sample, a blank of an equal volume provided, and all fourvolumes were treated ultrasonically for 2 minutes at 70 watts of power.

After the thus treated samples have cooled to room temperature, a volumeof the working dye solution described hereinbefore is added to eachsample in an amount equal to the 1:1 solvent-water solution addedthereto. The samples containing the dye are mixed thoroughly and allowedto stand and settle for 30 minutes.

After the mixed samples have settled, the supernatant is centrifugedfrom the solids and the separation completed by filtration. It was foundthat, because of the fineness of the particles in the sample, a simplefiltration was inappropriate because the pores of the filter mediumclogged and no flow was observed after a short time. While any finefilter paper is suitable it was found that a filter having about 0.45pores was eminently satisfactory for preparing the sample forspectroscopy.

An aliquot of the clear filtrate is removed and diluted with 1.5 volumesof a pH 4.2 acetate buffer and the absorbance determined at thewavelength appropriate for the dye employed. When bromocresol purple wasused the absorbance was determined at 422 ,u. in a Beckman model DUspectrophotometer. Other makes and models of spectrophotometers known tothose skilled in the art are equally adaptable to the determination ofthe absorbance.

The absorbance is determined on the filtrate from each of the twochrysotile spiked samples, the unspiked sample and the blank. The fourreadings are then plotted on arithmetic paper. While it is generally notimportant as to which of the elements is plotted as the abscissa andordinate, it is convenient to plot the mg chrysotile added as theabscissa and the absorbance as the ordinate. The absorbance obtained onthe blank is plotted as the baseline and the points plotted for theabsorbances of the three samples are connected by a best fittingstraight line and such line is extrapolated as a negative regressionline to the baseline. The mg chrysotile indicated on the abscissa at thepoint of intersection between the negative regression line and thebaseline is taken as the chrysotile content of the unspiked sample. Aconversion to a percent figure can be made in the usual way.

The accompanying graph depicts the actual construction of the graph todetermine the chrysotile content of a typical talc sample analyzed asdescribed in Example 1.

EXAMPLE 1 A stock solution of bromcresol purple was prepared bydissolving 0.15 g of the dye in 250 ml of 95 percent ethanol anddiluting such solution to 500 ml with water.

Twenty milliliters of the thus prepared stock was diluted to 250 ml byfirst adding 40 ml of 95 percent ethanol and then adding sufficient pH4.2 acetate buffer to make the 100 ml volume. This working dye solutionwas designed to yield an absorbance of 0.325 at 422 t, after beingfurther diluted 5 to l in the course of the test procedure describedimmediately below.

Pure chrysotile obtained from the Johns Manville Research Center,Manville, New Jersey 08835, was obtained for use in spiking the samplesof talc to be analyzed.

Three 0.2000 i 0.0010 g samples of talc were precisely and accuratelyweighed. One of the three samples was set aside to be analyzed withoutthe addition of spiking chrysotile. To one of the two remaining sampleswere added 3 mg of chrysotile and to the third sample were added 6 mg ofchrysotile, both precisely and accurately weighed.

To the two spiked and one unspiked samples of talc were added 10 ml of a1:1 95 percent ethanol water solution. There was also provided a blanksample of 10 ml of such solution. The three samples and the blank weregiven an ultrasonic treatment at watts for 2 minutes. Then the treatedsamples and blank were cooled to room temperature.

To each of the cooled samples and blank were added 10 ml of the workingbromcresol purple dye solution described above. Then the samples andblank were thoroughly mixed and allowed to settle for about 30 minutes,after which each was centrifuged. Following centrifugation, each of theliquids from the three samples and the blank were filtered through a0.45u millipore filter. A 10 ml aliquot of each filtrate was diluted to25 ml with pH 4.2 acetate buffer.

Optical absorbances were then determined at 422 ,u. on each of the fourdiluted filtrates employing a Beckman model DU spectrophotometer. Thesample representing the blank had an absorbance of 0.325. The unspikedtalc sample had an absorbance of 0.310, and the 3 mg and 6 mg chrysotilespiked talc samples had absorbances of 0.268 and 0.228 respectively.Plotting the mg chrysotile v absorbance on arithmetic paper yielded anindicated 1 mg of chrysotile as being present in the unspiked talcsample. This was equivalent to 0.5 percent.

What is claimed is:

1. A method for determining the chrysotile content of talc comprising:first, contacting said chrysotile containing talc with a solution of asulfonphthalein dye selected from the class consisting of bromphenolblue, bromthymol blue, bromcresol green, bromcresol purple, cresol red,and thymol blue, and measuring the optical absorbance of said solutionboth before and after contact with said talc; second, contacting atleast two additional samples of said talc, to which additional differingaccurately weighted quantities of chrysotile have been added, with asolution of said sulfonphthalein dye, and measuring the absorbance ofeach of said dye solutions after said contact; third, graphicallyrelating on an arithmetic scale the quantity of chrysotile added to saidtalc to the absorbance thus measured; and fourth, extrapolating anegative regression line through the points located on said graph to anintersection with a baseline representing the optical absorbance of saiddye solution before contact with such talc, said intersection pointindicating the chrysotile content of the tale.

2. The method of claim 1 wherein said solution is prepared by dissolvingsaid sulfonphthalein dye in a water miscible solvent selected from theclass consisting of methanol, ethanol, isopropanol and acetone to aconentration of from about 0.0125 to about 0.33 percent and then furtherdiluting said solution with water and an acidic buffer to provide a dyesolution that will yield an absorbance of from about 0.15 to about 0.75

at a wavelength appropriate to said dye after an additional :1 dilutionin the course of the test procedure.

3. The method of claim 2 wherein said water miscible solvent is ethanol.

4. The method of claim 2 wherein said acidic buffer is an acetate bufferat about pH 4.2.

5. The method of claim 1 wherein said sulfonphthalein dye is bromcresolpurple.

6. The method of claim 5 wherein said bromcresol purple is diluted to afinal concentration having an absorbance of about 0.325 at a wavelengthof about 422 7. The method of claim 1 wherein said solution is incontact with said chrysotile containing talc for about 30 minutes.

8. A method for determining the chrysotile content of talc comprisingthe steps of:

a. dissolving a sulfonphthalein dye selected from the class consistingof bromphenol blue, bromthymol blue, bromcresol green, bromcresolpurple, cresol red, and thymol blue in a suitable water miscible solventand diluting the resulting solution with an equal volume of water;

b. diluting the solution from (a) with an acidic buffer to aconcentration that will yield an absorbance of from about 0.15 to about0.75 at a wavelength consistent with the dye selected after a further5:1 dilution during the course of the test procedure;

0. weighing accurately three samples of talc to be analyzed to similarweights to the nearest 0.0010 g;

(1. adding to one of the three samples from (c) an accurately weightedquantity of chrysotile equal to from about 0.5 to about 2.5 percent byweight of said sample;

e. adding to a second of the three samples from (c) an accuratelyweighted quantity of chrysotile equal to about twice the concentrationby weight added to the sample in (d);

f. adding to the third of the three samples from (c) and to the samplesprepared in (d) and (e) a volume of a 1:1 solution of 95 percentethanolwater equal V/W to at least twice the weight of said sam- P g.providing a blank comprised of a volume of a 1:1

solution of percent ehtanol-water equal to the volume of said solutionadded to each of the three samples in (f);

h. subjecting the samples from (f) and the blank from (g) to anultrasonic treatment for about two minutes;

i. cooling the ultrasonically treated samples and blank from (h) to roomtemperature;

j. adding a portion of the dye solution from (b) to each of theultrasonic treated samples and blank from (i) in a volume equal to thevolume of the 1:1 ethanol-water solution added to said samples and usedas the blank;

k. mixing said dye solutions thoroughly with said samples and blank andallowing the dispersions produced thusly to stand for about 30 minutes;

1. separating the liquid from the dispersions of (k) by firstcentrifuging and then filtering to remove all suspended solids leaving aclear filtrate;

m. removing an aliquot from each of the filtrates of (1) and dilutingsaid aliquots with about 1.5 volumes of an acidic buffer;

11. measuring the optical absorbance of each of the diluted filtrates of(m) at a wavelength appropriate to the dye utilized in a suitablespectrophotometer;

0. plotting the absorbance against the amount of chrysotile added;

p. extrapolating a best fitting straight negative regression line to abaseline established as the absorbance of the blank of (g); and

q. determining the chrysotile concentration by reading the indicatedchrysotile content at the point where the negative regression lineintersects the baseline.

9. The method of claim 8 wherein the water miscible solvent of (a) isselected from the class consisting of methanol, ethanol, isopropanol andacetone.

10. The method of claim 9 wherein the water miscible solvent is ethanol.

11. The method of claim 8 wherein the sulfonphthalein dye is bromcresolpurple.

12. The method of claim 8 wherein the acidic buffer of b) and m) is anacetate buffer at a pH of about 4.2. =l

1. A METHOD FOR DETERMINING THE CHRYSOTILE CONTENT OF TALC COMPRISING:FIRST, CONTACTING SAID CHRYSOTILE CONTAINING TALC WITH A SOLUTION OF ASULFONPHTHALEIN DYE SELECTED FROM THE CLASS CONSISTING OF BROMPHENOLBLUE, BROMTHYMOL BLUE, BROMCRESOL GREEN, BROMCRESOL PURPLE, CRESOL RED,AND THYMOL BLUE, AND MEASURING THE OPTICAL ABSORBANCE OF SAID SOLUTIONBOTH BEFORE AND AFTER CONTACT WITH SAID TALC, SECOND, CONTACTING ATLEAST TWO ADDITIONAL SAMPLES OF SAID TALC, TO WHICH ADDITIONAL DIFFERINGACCURATELY WEIGHTED QUANTITIES OF CHRYSOTILE HAVE BEEN ADDED, WITH ASOLUTION OF SAID SULFONPHTHALEIN DYE, AND MEASURING THE ABSORBANCE OFEACH OF SAID DYE SOLUTIONS AFTER SAID CONTACT, THIRD, GRAPHICALLYRELATING ON AN ARITHMETIC SCALE THE QUANTITY OF CHRYSOTILE ADDED TO SAIDTALC TO THE ABSORBANCE THUS MEASURED, AND FOURTH, EXTRAPOLATING ANEGATIVE REGRESSION LINE THROUGH THE POINTS LOCATED ON SAID GRAPH TO ANINTERSECTION WITH A BASELINE REPRESENTING THE OPTICAL ABSORBANCE OF SAIDDYE
 2. The method of claim 1 wherein said solution is prepared bydissolving said sulfonphthalein dye in a water miscible solvent selectedfrom the class consisting of methanol, ethanol, isopropanol and acetoneto a conentration of from about 0.0125 to about 0.33 percent and thenfurther diluting said solution with water and an acidic buffer toprovide a dye solution that will yield an absorbance of from about 0.15to about 0.75 at a wavelength appropriate to said dye after anadditional 5:1 dilution in the course of the test procedure.
 3. Themethod of claim 2 wherein said water miscible solvent is ethanol.
 4. Themethod of claim 2 wherein said acidic buffer is an acetate buffer atabout pH 4.2.
 5. The method of claim 1 wherein said sulfonphthalein dyeis bromcresol purple.
 6. The method of claim 5 wherein said bromcresolpurple is diluted to a final concentration having an absorbance of about0.325 at a wavelength of about 422 m Mu .
 7. The method of claim 1wherein said solution is in contact with said chrysotile containing talcfor about 30 minutes.
 8. A method for determining the chrysotile contentof talc comprising the steps of: a. dissolving a sulfonphthalein dyeselected from the class consisting of bromphenol blue, bromthymol blue,bromcresol green, bromcresol purple, cresol red, and thymol blue in asuitable water miscible solvent and diluting the resulting solution withan equal volume of water; b. diluting the solution from (a) with anacidic buffer to a concentration that will yield an absorbance of fromabout 0.15 to about 0.75 at a wavelength consistent with the dyeselected after a further 5:1 dilution during the course of the testprocedure; c. weighing accurately three samples of talc to be analyzedto similar weights to the nearest 0.0010 g; d. adding to one of thethree samples from (c) an accurately weighted quantity of chrysotileequal to from about 0.5 to about 2.5 percent by weight of said sample;e. adding to a second of the three samples from (c) an accuratelyweighted quantity of chrysotile equal to about twice the concentrationby weight added to the sample in (d); f. adding to the third of thethree samples from (c) and to the samples prepared in (d) and (e) avolume of a 1:1 solution of 95 percent ethanolwater equal V/W to atleast twice the weight of said sample; g. providing a blank comprised ofa volume of a 1:1 solution of 95 percent ehtanol-water equal to thevolume of said solution added to each of the three samples in (f); h.subjecting the samples from (f) and the blank from (g) to an ultrasonictreatment for about two minutes; i. cooling the ultrasonically treatedsamples and blank from (h) to room temperature; j. adding a portion ofthe dye solution from (b) to each of the ultrasonic treated samples andblank from (i) in a volume equal to the volume of the 1:1 ethanol-watersolution added to said samples and used as the blank; k. mixing said dyesolutions thoroughly with said samples and blank and allowing thedispersions produced thusly to stand for about 30 minutes; l. separatingthe liquid from the dispersions of (k) by first centrifuging and thenfiltering to remove all suspended solids leaving a clear filtrate; m.removing an aliquot from each of the filtrates of (l) and diluting saidaliquots with about 1.5 volumes of an acidic buffer; n. measuring theoptical absorbance of each of the diluted filtrates Of (m) at awavelength appropriate to the dye utilized in a suitablespectrophotometer; o. plotting the absorbance against the amount ofchrysotile added; p. extrapolating a best fitting straight negativeregression line to a baseline established as the absorbance of the blankof (g); and q. determining the chrysotile concentration by reading theindicated chrysotile content at the point where the negative regressionline intersects the baseline.
 9. The method of claim 8 wherein the watermiscible solvent of (a) is selected from the class consisting ofmethanol, ethanol, isopropanol and acetone.
 10. The method of claim 9wherein the water miscible solvent is ethanol.
 11. The method of claim 8wherein the sulfonphthalein dye is bromcresol purple.
 12. The method ofclaim 8 wherein the acidic buffer of b) and m) is an acetate buffer at apH of about 4.2.